Coil System and Method for Obtaining Volumetric Physiological Measurements

ABSTRACT

A coil device is provided having a member adapted to extend around and conform to an outer surface of a subject and a conductor adapted to extend only once around a first portion of the subject. The coil device can be positioned about the subject in order to measure a volume of the subject. When placed about the subject in the presence of a relatively homogeneous magnetic field, the conductor can generate a signal indicative of a volume of the first portion of the subject. The coil device may also include two or more conductors separately generating signals indicating volumes of two or more corresponding portions of the subject. In some cases the coil device includes associated authorization data that can limit use of the coil device. Systems and methods incorporating the coil device are also provided.

BACKGROUND

Many applications exist in which the accurate measurement of one or moredynamic volumes is desirable. For example, in the field of physiology,medical doctors, researchers and others use volumetric measurements tomonitor and characterize physiological functions within a subject (e.g.,a human patient), and diagnose ailments thereof.

One specific example includes the measuring of breathing volumes inpatients. Respiratory disease is a common and significant problem inboth the United States and throughout the world. Obstructions can stemfrom the constriction of the airways caused by inflammation and edema ofthe walls of the terminal bronchi, or narrowing of the trachea or thethroat. Obstructions in the distal airways generally make expirationslower and/or more difficult as more air is exhaled from the lungs orduring the latter part of expiration, while upper airway obstructionmight provide a more constant resistance to air flow. Types ofrespiratory disease include diseases of the lung, bronchial tubes,pleural cavity, upper respiratory tract, trachea, and of the nerves andmuscles of breathing. An important step in monitoring for and managingsuch diseases, as well as less severe respiratory conditions, involvesmeasuring air flow volumes moving into and out of the patient's lungs.

Recording breathing volumes is commonly performed through the use of avolume flow-sensing device connected to a subject's airway (e.g., aspirometer or tachymeter), although such devices can be overlyintrusive. Another method for measuring breathing volumes includesmeasuring the movements of the subject's chest and abdominal walls.These techniques are often strain gauge based (i.e., determining changesin body circumference) or based on elastic inductive electricalconductor loops arranged around the chest and abdomen of the subject.Changes in body circumference, or recordings of the inductance of theloops, can then be used to estimate the magnitude of cross sectionalarea and volume variations of the chest and abdominal compartments.

The strain gauge or circumferential distance methods have no simple orreproducible relation between the measured variations and the volumesthat are measured. This relation depends on assumptions about therelation between the area enclosed by the loop and the length of theloop that are valid only for a fixed geometry. Although some of themethods based on inductance may claim that area is measured (i.e., it isassumed to be proportional to loop inductance), the assumption is onlyvalid as long as the relative shape of the loop is conserved.Unfortunately, this is not the case for the cross-sectional areavariations of, e.g., the human chest or abdomen that occur duringrespiration.

In response to these and other drawbacks of past methods of measuringvolumes, VoluSense, the assignee of the present invention, has developednew systems and methods for measuring volumes, including the use of avolume-sensing element and associated electromagnetic inductiontechniques. Some of these systems and methods are disclosed inVoluSense's U.S. Pat. Nos. 6,374,667; 6,945,941; and 7,390,307, thecontents of which are hereby incorporated by reference herein in theirentirety.

The electromagnetic induction techniques described in these patentsprovide a measurable advance over past methods of measuring volumes.However, VoluSense continuously looks for ways to optimize equipment,methods, and other aspects of its existing systems, as will becomeapparent throughout the remainder of this disclosure.

SUMMARY

Embodiments of the invention relate to devices, systems and methods formeasuring static and dynamic volumes, such as, for example, a volume ofa subject's abdomen and/or chest. Embodiments of the invention providesimplified and improved techniques that employ a single conductorextending only once around a subject to measure a volume of the subjectwithin a relatively homogeneous magnetic field. Some embodiments of theinvention also provide a common area on a coil device where multipleconductors can exit the coil device, thus providing a coil device thatcan be easily wrapped about a subject to measure a volume. In addition,some embodiments of the invention provide an advantageous use ofauthorization data that can limit or otherwise control use of aparticular coil device.

In some embodiments, a coil device is provided that can be positionedabout the subject (e.g., a patient) in order to measure one or morevolumes of the subject. The coil device includes a first member adaptedto extend around and conform to an outer surface of a first portion ofthe subject despite changes in a contour of the outer surface. The firstmember can include a first conductor that is adapted to extend only oncearound the first portion of the subject. In some cases, the firstconductor is adapted to generate a signal indicative of a volume of thefirst portion of the subject in the presence of a relatively homogeneousmagnetic field such as that produced by an electromagnet energized withan alternating current.

In some embodiments, a coil device is provided that includes a firstmember adapted to extend around an outer surface of a first portion of asubject. The first member includes a first conforming means thatconforms the first member to the outer surface of the first portion. Thefirst member also includes a first conducting means. The conductingmeans can generate, in the presence of a relatively homogeneous magneticfield, a signal indicative of a volume of the first portion of thesubject. In some cases, the first conducting means comprises a singleconductor adapted to extend only once around the first portion of thesubject.

According to another aspect of the invention, a method for measuring avolume of a subject is described. The method includes providing a coildevice with a first member having a first conductor and extending thefirst member around an outer surface of a first portion of the subject.The first member conforms to the outer surface despite changes in acontour of the outer surface. Further, in some cases, the methodincludes extending the first conductor only once around the firstportion of the subject. A relatively homogeneous magnetic field isgenerated within a predefined spatial volume and the first portion ofthe subject is positioned within the spatial volume. After positioningthe subject and generating the magnetic field, the method includesmeasuring a signal induced in the first conductor by the magnetic fieldand estimating a volume of the first portion of the subject based on themeasured signal.

In some embodiments, the coil device includes an electronic memorystoring authorization data, and the method further includes reading theauthorization data from the electronic memory and determining from theauthorization data whether use of the coil device is authorized. If useof the coil device is authorized, the method may further includeestimating a volume of the first portion of the subject based on asignal induced in the first conductor.

According to another aspect of the invention, in some embodiments, asystem for measuring a volume of a subject is provided. The systemincludes an electromagnet able to generate a relatively homogeneousmagnetic field and a coil device having an electronic memory storingauthorization data. In some cases the coil device is adapted to conformto an outer surface of a first portion of the subject and generate asignal indicative of a volume of the first portion of the subject in thepresence of the relatively homogeneous magnetic field. The systemfurther includes a control system electrically coupled to the coildevice. The control system is adapted to read the authorization datafrom the electronic memory, determine from the authorization datawhether use of the coil device is authorized, measure the signalgenerated by the first conductor, and estimate the volume of the firstportion of the subject based on the signal received from the firstconductor if use of the coil device is authorized.

Embodiments of the invention provide a number of advantages overconventional devices and methods for measuring a volume of a subject.For example, embodiments of the invention provide a simplified coildevice capable of measuring a volume of a subject with a singleconductor that only extends once around the subject. This simplifieddesign can be easier and cheaper to manufacture than existing coildevices that measure volume with multiple conductors or multiple turnsof a single conductor. In addition, in some embodiments a coil devicecan be easily wrapped around a subject and coupled to a measuring systemdue to the lack of multiple conductors or turns and connectionsassociated with past coil devices. In some cases, a coil device isprovided with a return conductor that allows all electrical connectionsto the coil device to be collected in one common area before exiting thecoil device. Such a configuration can also aid in placing a coil deviceabout a subject and/or removing it with ease. Some embodiments of theinvention provide a number of advantages associated with the use ofauthorization data. In some cases authorization data associated with aparticular coil device can be used to determine whether use of the coildevice is authorized. For example, use of a particular coil device maybe limited to a predefined number of uses or to an individual patient.Thus, use of the coil device can be limited for a variety of reasons. Asjust some examples, use may be limited due to sanitation concerns orwear on the coil device, or alternatively, for consistency with aparticular business model.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of thepresent invention and therefore do not limit the scope of the invention.The drawings are not to scale (unless so stated) and are intended foruse in conjunction with the explanations in the following detaileddescription. Embodiments of the present invention will hereinafter bedescribed in conjunction with the appended drawings, wherein likenumerals denote like elements.

FIG. 1 is a perspective view of a coil device formed into a shape formeasuring a volume of a subject according to an embodiment of theinvention.

FIG. 2 is a perspective view of the coil device of FIG. 1 placed arounda subject according to an embodiment of the invention.

FIG. 3 is a top view of the coil device of FIG. 1 spread out and laidflat.

FIG. 4 is a side view of the coil device of FIG. 1.

FIG. 5 is a perspective view of a coil device formed into a shapeaccording to another embodiment of the invention.

FIG. 6 is a top view of the coil device of FIG. 5 spread out and laidflat.

FIG. 7 is a perspective view of the coil device of FIG. 5 placed arounda subject according to an embodiment of the invention.

FIG. 8 is a top view of a coil device spread out and laid flat accordingto another embodiment of the invention.

FIG. 9 is a perspective view of the coil device of FIG. 8 placed arounda subject according to an embodiment of the invention.

FIG. 10 is a schematic of a coil device connector according to anembodiment of the invention.

FIG. 11 is a schematic of a system for measuring a volume of a subjectaccording to an embodiment of the invention.

FIG. 12 is a flow diagram illustrating a method for measuring a volumeof a subject according to an embodiment of the invention.

FIG. 13 is a flow diagram illustrating a method for authorizing themeasurement of a volume of a subject according to an embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical illustrations for implementing exemplary embodiments of thepresent invention. Examples of constructions, materials, dimensions, andmanufacturing processes are provided for selected elements, and allother elements employ that which is known to those of skill in the fieldof the invention. Those skilled in the art will recognize that many ofthe examples provided have suitable alternatives that can be utilized.

FIG. 1 is a perspective view of a coil device 10 useful for measuringvolume with electromagnetic induction techniques according to anembodiment of the invention. The coil device 10 includes a first member12 that is adapted to extend around an object (e.g., a patient) having avolume to be measured. The first member 12 comprises a configuration ofa first conductor 14 that extends around the object. In someembodiments, the first member 12 is carried by a substrate 15 useful forsecuring the first member 12 about the object. In use, when the coildevice 10 and object are placed within a magnetic field, the coil device10 generates a signal corresponding to a volume of the object. Forexample, a relatively homogeneous magnetic field can induce a signal inthe first conductor that indicates the volume of the object. The inducedsignal can then be measured to determine the volume. As used herein, thephrases “measuring volume” and “measure a volume” encompass both theconcept of quantifying a physical signal directly signifying a volume,as well as quantifying a signal and then calculating, estimating, orotherwise determining a volume based on the quantified signal.

The coil device 10 can be useful for measuring volumes of a variety ofobjects, including those with irregularly-shaped volumes and/or volumesthat change over time. In some cases, the coil device 10 can be usefulfor measuring changes in volume. For example, as shown in FIG. 2, thecoil device 10 can be placed about the chest and/or abdomen of a subject16 to measure a breathing volume, or a change in the breathing volume,of the subject 16. In additional embodiments, the coil device 10includes an electronic memory (not shown in FIG. 1 or 2) storingauthorization data. As will be described in more detail, theauthorization data can provide a secure environment and ensure that onlyauthorized uses of the coil device 10 are allowed. For example, eachcoil device may be limited to a specified subject or number of uses.

Embodiments of the coil device 10 can be especially useful for measuringbreathing volumes of human subjects, including fully grown adults,adolescents, and, as shown in FIG. 2, infants. Such volume measurementscan aid in characterizing respiratory conditions and diagnosingrespiratory diseases, but can also be helpful in a wide variety ofapplications, including, but not limited to physiological research. Inaddition, while embodiments of the invention are discussed herein withreference to human subjects, the embodied devices, systems, and methodsare equally applicable to non-human subjects.

Returning to FIGS. 1 and 2, the first member 12 of the coil device 10includes a configuration of the first conductor 14 extending around thevolume to be measured. In some embodiments the configuration of thefirst conductor 14 defines a first edge 18 and an opposed, second edge20 of the first member 12. For example, referring to FIG. 2, the firstmember 12 may be positioned about the subject 16 so that the firstmember's first edge 18 is nearer the subject's head, while the secondedge 20 is nearer the subject's feet. A distance between the first edge18 and the second edge 20 can be considered the width of the firstmember 12.

In some embodiments, the configuration of the first conductor 14 alsodefines a first end section 22 and an opposed second end section 24 ofthe first member 12. Referring to FIG. 2, the first end section 22 ispositioned proximate to the opposed second end section 24 as the firstmember 12 wraps around the subject 16. Thus the first conductor 14 alsoextends about the subject. In some cases the first member 12 may fullywrap around the subject's torso so that its first and second endsections 22, 24 are positioned closely adjacent each other as shown inFIGS. 1 and 2, while in other cases, the first and second end sections22, 24 may be separated by some amount, so that the first member 12extends less than completely about the subject 16. A distance betweenthe first and second end sections 22, 24 can be considered the length ofthe first member 12.

In some embodiments, the first member 12 (and any optional substrate 15)can have a planar configuration that is wrapped about the subject 16 tomeasure volume. FIG. 3 illustrates a top planar view of the coil device10 spread out and laid flat when not wrapped around the subject 16. FIG.3 illustrates the opposed edges 18, 20 of the first member 12 and theopposed end sections 22, 24 according to one embodiment. In someembodiments, the first conductor 14 is configured to include a number ofangled segments 26 extending substantially between the first and secondopposed edges 18, 20 at multiple points. For example, the angledsegments 26 may form the first conductor 14 in a zigzag pattern orconfiguration. The angled segments 26 are preferably straight, ofsubstantially the same length and formed at identical, symmetricalangles, although these may not be necessary. For example, in someembodiments the angled segments 26 may have varying lengths and/orangles such that the width W of the first member 12 varies along itslength L.

In one embodiment, the first conductor 14 includes at least thirtyangled segments 26. In some such embodiments, the first conductor 14crosses back and forth at least fifteen times from the first end section22 to the second opposed end section 24. The number of angled segments26 may vary depending upon a variety of factors including the size ofthe subject and the measurement accuracy desired. For example, thenumber of angled segments 26 may be less or more than thirty. In somecases, the strength of the correlation between the induced signal andthe volume of the subject 16 to be measured increases as the number ofangled segments 26 between the first and second opposed end sections 22,24 increases.

Returning to FIG. 2, in some embodiments the first member 12 is adaptedto extend around an outer surface of a first portion 30 of the subject'sabdomen and/or chest. For example, the width of the first member 12 maybe great enough to cover substantially all of the subject's abdomen andchest, as shown in FIG. 2. In other cases, the first member 12 may onlyextend around all or only a portion of the subject's abdomen or all oronly a portion of the subject's chest. Those skilled in the art willappreciate that a variety of configurations are possible, and mayinclude configurations for other portions of the subject's body as well.

The first member 12 can conform to the outer surface of the firstportion despite changes in the contour of the outer surface. Suchcontour changes can result in a varying cross-sectional area of thefirst portion 30 between the first and second edges of the first member.For example, the outer surface of the first portion 30 may be formed ina somewhat variable and irregular shape, and include the naturalcontours of the subject's torso, e.g., widening at the hips and chest.In addition, the contour of the subject's outer surface may change whilethe subject 16 breathes and the subject's chest and/or abdomen rise andfall. Accordingly, in some embodiments movement of the first member isrepresentative of movement of the underlying portion of the subject 16.

According to some embodiments of the invention, when the subject 16 andthe coil device 10 are placed within a relatively homogeneous,time-varying magnetic field, the first conductor 14 generates a signalindicative of a volume of the first portion 30 of the subject 16. Thefirst conductor 14 can in some cases be considered the magneticequivalent of a single, planar loop having a cross-sectional area equalto the average cross-sectional area of the first portion 30. In thisembodiment the first conductor 14 generates a signal corresponding tothe average cross-sectional area of the first portion 30. This signalcan then in turn be used to measure the volume of the first portion 30of the subject 16.

In some cases the induced signal (e.g., a voltage) is related to thevolume of the first portion 30 by a proportionality constant. Forexample, the signal generated by the first conductor 14 may beproportional to the volume of the first portion 30 by an approximateproportionality constant equal to the width W of the first member 12(i.e., the distance between the first and second opposed edges 18, 20 ofthe first member). Thus, in some embodiments, the induced signal isrelated to the configuration of the first conductor's angled segments26.

As will be appreciated from the discussion and figures herein,embodiments of the invention are useful for measuring volumes with asingle turn or winding of a single conductor. Referring to FIG. 2,according to some embodiments the first conductor 14 extends only oncearound the first portion 30 of the subject of the coil device 10. Anelectrical connector 32 coupled with the ends of the first conductor 14can provide a convenient manner for coupling the coil device 10 withmeasuring equipment. Thus embodiments of the coil device 10 include asimpler configuration for measuring or estimating volumes, especiallywhen compared to devices with multiple windings of a single conductor,or single turns of multiple conductors.

As shown in FIG. 2, in some embodiments the first member 12 conforms tothe outer surface of the first portion 30 of the subject 16. In somecases the optional substrate 15 assists the first member 12 inconforming to the outer surface of the first portion 30. In otherembodiments, the first member 12 can have inherent material propertiesthat assist in conforming to the outer surface of the first portion 30.

For example, the first member 12 can itself have stretchable propertiesthat provide a close, conforming fit around the subject 16 without theuse of a separate substrate. In some cases the first member 12 may bemanufactured from a material with an inherent spring constant or otherelastic properties. In another embodiment, the angled segments 26 of thefirst member 12 may stretch apart at their common joints, thusincreasing the angles between adjacent segments 26 and stretching thefirst member 12 to the necessary degree to extend around and conform tothe outer surface of the first portion 30 of the subject 16.

Referring to FIGS. 1-3, in another embodiment, the coil device 10 caninclude the substrate 15 that carries the first member 12 and ensuresthat the first member 12 conforms to the subject. In some embodimentsthe substrate 15 has elastic or other stretchable qualities, similar insome cases to spandex or rubber. The first conductor 14 may be fastenedto the substrate in a variety of manners, including using plasticwelding, glue, stitching, or any other means known in the art. In somecases, the first conductor 14 may be fastened by incorporating it intothe substrate during the weaving or manufacture of the substrate.

In some embodiments, the substrate 15 can take the form of a planarsheet that can be wrapped about the first portion 30 of the subject 16.For example, referring to FIGS. 2 and 3, the substrate 15 may have afirst edge 34 and an opposing second edge 36, with the first edge 34nearer the subject's head and the second edge 36 nearer the subject'sfeet. As shown in FIG. 3, the substrate 15 can also include a first endsection 38 and an opposing second end section 40. As shown in FIGS. 3and 4, the first and second end sections 38, 40 of the substrate 15 (aswell as the first and second end sections, 22, 24 of the first member)are adapted to be positioned proximate one another as the substrate 15and the first member 12 extend around the first portion 30 of thesubject.

Once positioned, the first and second end sections can be secured toconform the substrate to the outer surface of the first portion 30. Forexample, in some cases the first and second end sections 38, 40 of thesubstrate may be secured directly to the subject 16 with e.g., anadhesive tape. In another embodiment, the substrate 15 includes afastener 42 for fastening the first end section 38 to the second endsection 40. For example, the fastener 42 may include a variety offasteners, such as hook-and-loop, adhesive, snaps, zippers, buttons,and/or staples.

Referring to FIG. 4, in some embodiments the first and second endsections 38, 40 of the substrate 15 can be secured in a number ofpositions to provide an adjustable substrate able to accommodatedifferently sized subjects. For example, in one case the substrate'sfirst end section 38 can be secured at multiple points along theinterior surface of the substrate's second end section 40, providing anincreasingly snug fit. In some embodiments any unused “flap” of thesubstrate 15 at the second end section 40 may be tucked underneath thesubject 16 such that it is less likely to move as the subject 16breathes. This may increase the signal accuracy of the coil device 10.

While the substrate 15 is shown in FIGS. 1-4 as a planar body that maybe wrapped about the subject 16, other configurations are possible andthe invention is not limited to any single configuration. For example,in some embodiments, the substrate 15 may be configured in the shape ofa continuous sleeve or other similar shape that can be positioned aboutthe subject 16 by pulling it over the subject's head or legs.

The substrate 15 comprises a stretchable material such as spandex orrubber, and in some embodiments can be formed from an elastic medicalbandage material. In some embodiments, an electrically insulating layerof material is preferably positioned over the substrate 15 and the firstconductor 14. The first conductor 14 may comprise any electricallyconducting material known in the art. For example, the first conductormay comprise copper. In another embodiment, the first conductor 14 maybe stamped or cut from a thin metal foil sheet (e.g., aluminum). In somecases this can provide an easily constructed and disposable coil device.

As will be appreciated from the discussion and figures herein,embodiments of the invention are useful for measuring volumes with asingle turn or winding of a single conductor. Thus the coil device 10includes a less complex configuration for measuring a volume of thefirst portion 30 of the subject 16 when compared to devices withmultiple windings of a single conductor, or with single turns ofmultiple conductors. For example, with only a single conductor ratherthan multiple conductors, the coil device 10 requires fewer electricalconnections that in past designs. Fewer electrical connections cansimplify the measurement process by, for example, making the coil device10 easier to place around and remove from a subject. In addition, thesingle turn of the first conductor 14 allows a simpler and lessexpensive production process for manufacturing the coil device 10,especially when compared with devices including multiple conductors formeasuring volume.

Turning now to FIGS. 5-7, various views are shown of a coil device 100having multiple conductors for measuring multiple independent volumes ofthe subject 16. The coil device 100 includes a first member 102 having afirst conductor 104 for measuring a volume of a first portion 106 of thesubject 16. The coil device 100 further includes a second member 122with a second conductor 124 for measuring a volume of a second portion126 of the subject 16. The first and second members 102, 122advantageously allow independent measurement of two separate volumes.For example, as shown in FIG. 7, in some cases the first member 102 canbe positioned around part or all of the subject's chest and the secondmember 122 can be positioned around part or all of the subject'sabdomen. Such a configuration can be useful for detecting when thesubject's abdomen moves in asynchrony with the subject's chestindicating an asynchronous breathing pattern. In addition, the volumesof the first and second portions can be summed to estimate the tidalbreathing volume of the subject 16.

The first member 102, first conductor 104, second member 122 and secondconductor 124 have features similar and generally corresponding to thefirst member 12 and first conductor 14 of the coil device 10 depicted inFIGS. 1-4. For example, the first member 102 has first and second edges108, 110 and the second member 122 has first and second edges 128, 130.In addition, the first member 102 has a first end section 112 and asecond end section 114, while the second member 122 also includes afirst end section 132 and a second end section 134. Each of the firstand second conductors 104, 124 includes a number of angled segments 116,136, respectively, that substantially extend between the respectivefirst and second edges of each member.

According to some embodiments of the invention, when the subject 16 andthe coil device 100 are placed within a relatively homogeneous,time-varying magnetic field, the first conductor 104 generates a signalindicative of a volume of the first portion 106 of the subject 16 andthe second conductor 124 generates a signal indicative of a volume ofthe second portion 126 of the subject 16. Each conductor can in somecases be considered the magnetic equivalent of a single, planar loophaving a cross-sectional area equal to the average cross-sectional areaof the first portion 106 and the second portion 126, respectively. Thesignals generated correspond to the average cross-sectional areas andcan then in turn be used to measure the volumes of the first and secondportions 106, 126 of the subject 16.

In some cases the induced signal (e.g., a voltage) in each conductor isrelated to the measured volume by a proportionality constant. Forexample, referring to FIG. 6, the signal generated by the firstconductor 104 may be proportional to the volume of the first portion 106by an approximate proportionality constant equal to the width W1 of thefirst member 102 (i.e., the distance between the first and secondopposed edges 108, 110 of the first member). Similarly, the signalgenerated by the second conductor 124 may be proportional to the volumeof the second portion 126 by an approximate proportionality constantequal to the width W2 of the second member 122 (i.e., the distancebetween the first and second opposed edges 128, 130 of the secondmember).

The coil device 100 can be coupled with a control system as desired byleads extending from the end sections of the first and secondconductors. In some cases each of the first and second conductors 104,124 may be coupled individually to the larger system or possibly by ashared common return conductor. For example, referring to FIG. 6, insome embodiments the first conductor can be coupled to the larger systemby a first lead 117 at the first end section 112 of the first member 102and a return lead 118 at the second end section 114 of the first member102. The second conductor can be similarly coupled to the system by asecond lead 127 at the first end section 132 of the second member 122and the same return lead 118 also at the second end section 134 of thesecond member 122. Referring to FIG. 7, a single connector 32 may couplethe leads to the system together, or alternatively, the leads may beindividually coupled to the system. Depending upon the desiredconfiguration, the leads 117, 118, and 127 can comprise an integralportion of the one or more of the first and second conductors or mayinclude separate, individual wires coupled to one or more of the firstand second conductors.

As with the coil device 10 of FIGS. 1-4, the coil device 100 of FIGS.5-7 can conform to the outer surface of the first and second portions ofthe subject despite changes in the contour of the outer surface. In somecases an optional substrate 135 assists the first and second members102, 122 in conforming to the outer surface. In some embodiments, thefirst and second members can have inherent material properties thatassist in conforming to the outer surface of the subject 16.

For example, the first and second members 102, 122 can themselves havestretchable properties that provide a close, conforming fit around thesubject 16 without the use of a separate substrate. In some cases thefirst and second members may be manufactured from a material with aninherent spring constant or other elastic properties. In anotherembodiment, the angled segments 116, 136 may stretch apart at theircommon joints, thus increasing the angles between adjacent segments andstretching the first and second members to the necessary degree toextend around and conform to the outer surface of the first and secondportions 106, 126 of the subject 16, respectively.

Referring to FIGS. 5-7, in another embodiment, the coil device 100includes the single substrate 135 that carries both the first and secondmembers and ensures that the members conform to the subject. In someembodiments the substrate 135 has elastic or other stretchablequalities, similar in some cases to spandex or rubber. The conductors104, 124 may be fastened to the substrate in a variety of manners,including using plastic welding, glue, stitching, or any other meansknown in the art.

As shown in FIGS. 5-7, the substrate 135 can in some embodiments takethe form of a planar sheet that can be wrapped about the first andsecond portions 106, 126 of the subject 16. Once positioned, first andsecond end sections 140, 142 of the substrate can be secured to conformthe substrate to the outer surface of the subject 16. For example, insome cases the end sections may be secured directly to the subject 16.In some cases, the substrate 135 includes a fastener 138 for fasteningthe end sections of the substrate together.

In addition, while the substrate 135 is shown as a planar body that maybe wrapped about the subject 16, other configurations are possible andthe invention is not limited to any single configuration. For example,in some embodiments, the substrate 135 may be configured in the shape ofa continuous sleeve or other similar shape that can be positioned aboutthe subject 16 by pulling it over the subject's head or legs.

As will be appreciated, a wide variety of configurations of the firstand second members 102, 122 are possible. For example, in someembodiments of the invention, the first and second members 102, 122 mayshare the same substrate 135, while in other cases the first member 102may be carried by a first substrate and the second member 122 may becarried by a second substrate. Also, the first and second members 102,122 may be positioned adjacent one another, as in FIG. 7, or some gapmay be provided between the first and second members according to thedesired portions of the subject to be measured. At least in oneembodiment, the first member 102 is adapted to extend around at least aportion of the subject's chest, and the second member 122 is adapted toextend around at least a portion of the subject's abdomen.

Referring to FIGS. 8-9, in some embodiments a third return conductor 150is provided for coupling the first and second conductors 104, 124 to acontrol system. For example, with respect to FIG. 8, the third conductor150 may be coupled to the first and second conductors 104, 124 proximatethe second end section 142 of the substrate 135. The common thirdconductor 150 then extends back along the substrate 135 towards thefirst end section 140 of the substrate 135 and is coupled to (oralternatively integral with) the common return lead 118. When using thisarrangement, the voltage that is induced in the common third conductor150 will be subtracted from the voltage induced in the first and secondconductors. In some embodiments, the third conductor 150 is located overa body portion that does not change its volume during respiration. Thispositioning can increase the accuracy of measurements of respiratoryvariations in the volumes of body portions covered by the first andsecond conductors.

As shown in FIG. 8, the configuration in this embodiment allows allthree conductors to exit the substrate 135 via leads 117, 118, and 127at a common area proximate the first end section 140 of the substrate135. Referring to FIG. 9, this configuration provides a simplifiedwiring scheme with a common coupling point at the connector 32 andallows the coil device 100 to be easily wrapped around the subject 16without tangling or pulling at leads exiting from opposite end sectionsof the substrate.

As shown in FIG. 9, in some embodiments the common third conductor 150is adapted to extend around an outer surface of a third portion 152 ofthe subject 16. In some cases, the third portion 152 of the subject 16preferably has a relatively constant volume which does not change duringrespiration. For example, FIG. 9 depicts the third conductor 150extending around an area near the hips of the subject 16. Such anarrangement allows the signal induced in the third conductor by themagnetic field to be more easily separated from the desired signalsinduced in the first and second conductors, thus providing an accuratemeasurement of the volume variations in body parts covered by the firstand second conductors as previously mentioned.

In addition, in some cases the third conductor 150 provides anadditional advantage for noise cancellation. As will be appreciated,noise from external sources induces noise signals in the first, second,and third conductors of the coil device 100. Because the third conductor150 extends around the subject 16 in the opposite direction from thefirst and second conductors, noise signals originating from externalmagnetic fields induced in the third conductor 150 will have a polarityopposite of noise signals induced in the first and second conductors.These signals of opposite polarity will have a tendency to cancel eachother, and thus some embodiments of the coil device provide enhancednoise performance.

In additional embodiments, any of the coil devices 10, 100 can includean electronic memory storing authorization data for determining whetheruse of the coil device is authorized. Referring now to FIG. 10, in somecases an electronic memory 160 is provided within the connector 32. Anyother suitable placement, including on the coil device substrate, can beused depending upon the desired configuration. Placing the electronicmemory 160 within the connector 32 can provide a convenient connectionpoint for securing the memory 160 within the coil device whileminimizing electrical connections and wire lengths.

The connector 32 can be provided in any number of the wide variety offorms available in the art. In one embodiment, the connector 32 isprovided as a 6P6C plug, which conveniently provides three lines for thethree leads 117, 118, 127, and three dedicated lines for the electronicmemory 160. The memory 160 can be provided in a wide variety of formatsand sizes. In some cases the memory 160 is configured as TO-92 packagewith three leads and with 1024 bits. In at least one embodiment theelectronic memory 160 is a programmable read-only memory, which allowsthe connected control system to write to the memory 160 once and thenread it many times.

The authorization data within the electronic memory 160 can comprise avariety of information. In some embodiments the authorization datalimits the number of uses of the coil device. For example, theauthorization data may include a maximum count corresponding to themaximum number of authorized uses allowed for the coil device. Theauthorization data may also include a current count that can be comparedto the maximum count to determine if use of the coil device isauthorized. The authorization data may also include a stored identifiercorresponding to a particular subject that may be authorized to use thecoil device.

As will be discussed in further detail, the authorization data can beimplemented into volume measurement procedures in a variety of ways. Forexample, when an operator, such as a laboratory technician connects aparticular coil device to a control system, the control system canretrieve the authorization data from the coil device and determine ifuse of the device is authorized. If use is authorized, the operator canthen place the coil device around a subject and measure the desiredvolume. Alternatively, if use is not authorized, the control system can,for example, display an error message and stop the measurement process.

Accordingly, the authorization data can limit use of a particular coildevice when desirable. For example, in some embodiments a coil devicemay be provided in a disposable, single-use form. In this case, it maybe desirable to limit the coil device to a single use in accordancewith, for example, sanitation policies or business practices, and/orbecause of ordinary wear and tear on the coil device. The number ofauthorized uses can be adjusted to any suitable number as desired. Also,it may be desirable to limit use of a reusable coil device to a singlesubject, again due to, for example, sanitation and/or a particularbusiness model.

In addition to or instead of authorization data, the electronic memory160 may include a wide variety of other information. For example, insome embodiments the electronic memory 160 stores one or moreproportionality constants corresponding to one or more members of thecoil device as previously explained. A control system coupled to thecoil device can retrieve the proportionality constant(s) from the memoryand use them with the induced signal(s) measured from the conductor(s)to estimate the one or more volumes of the subject.

FIG. 11 is a schematic of a system 200 for measuring one or more volumesof the subject 16 according to some embodiments of the invention. Ingeneral, the system 200 includes the coil device 100, a control system201, and an electromagnet 202 for generating a relatively homogeneousmagnetic field. Although the coil device 100 is depicted, a coil deviceaccording to any embodiment of the invention may similarly be usedwithin the system 200.

The control system 200 may include a variety of elements similar in manyrespects to the systems described in U.S. Pat. Nos. 6,374,667;6,945,941; and 7,390,307, which are hereby incorporated by referenceherein in their respective entireties. For example, in some embodiments,the system integrates into a single system both the current source thatpowers the electromagnet 202 and the circuits needed to amplify andrectify the signals measured from the coil device 100. In some cases thecomponents of the control system 200 may be implemented in hardware,firmware, and/or software depending upon the particular application andoperating environment. For example, in some cases portions of thecontrol system 200 may be implemented in hardware, such as on adedicated circuit board, and other portions may be implemented inexecutable software instructions, either on the dedicated circuit board,or within a computer (e.g., a personal laptop computer) coupled with thededicated board. Those skilled in the art will appreciate a variety ofimplementations other than these particular examples are possible.

The current source includes an alternating current signal generator 204and power amplifier 206 that feed the electromagnet 202. Theelectromagnet 202 can take a variety of forms. For example, theelectromagnet 202 can include one of the electromagnets described inU.S. Pat. Nos. 6,374,667; 6,945,941; and 7,390,307. Once energized, theelectromagnet 202 generates a relatively homogeneous, time-varying fieldwithin a predefined spatial volume 208. For example, the field may havea coefficient of variation of less than five percent throughout thespatial volume 208. The electromagnet 202 is typically configured andpositioned such that the predefined spatial volume 208 is positionedproximate to a subject support surface for measuring a volume of thesubject 16 resting upon the support surface. For example, theelectromagnet 202 may be positioned to generate the magnetic fieldwithin the spatial volume 208 proximate a crib, an incubator, a bed, oranother suitable platform supporting the subject 16.

The signals induced in the members of the coil device 100 are fed intoparallel processing paths in one embodiment. For example, as shown inFIG. 11, the signals are fed to corresponding amplifiers 210, 212, andthen to corresponding switched rectifiers 214, 216. The gain of theamplifiers need not be more than necessary to suppress the noise of therectifiers, with a typical value of about 20 to 25 dB. The switchedrectifiers 214, 216 rectify the alternating voltage signals, and areeasily implemented by CMOS analog switches. Upon being rectified, thesignals are fed to corresponding low-pass filters 218, 220 for furtherprocessing.

In some embodiments, the signals exiting the low-pass filters 218, 220generally correspond to the average cross-sectional areas of the firstand second members of the coil device 100, respectively. The controlsystem 200 may retrieve one or more proportionality constants stored inelectronic memory associated with the coil device 100 (e.g., locatedwithin connector 32) and use these to estimate the volumes of thesubject 16 in multipliers 222, 224. The multipliers 222, 224 may beimplemented in hardware, firmware, and/or software depending upon theparticular environment and operating environment. The resulting signals,in this case indicating a volume of the subject's chest (thorax) andabdomen, are then available for output or further processing if desired.

In some embodiments, the control system 200 further includes anauthorization module 230 that may communicate with the optionalelectronic memory of the coil device 100. The authorization module 230retrieves authorization data from the electronic memory and is adaptedto determine whether use of the coil device 100 is authorized. Forexample, the authorization module 230 may compare a current count ofauthorized uses with a maximum count of authorized uses allowed for thecoil device stored within the electronic memory. The authorizationmodule 230 may further compare a subject identifier with a storedidentifier to determine if use of the coil device 100 is authorized fora particular subject.

Of course, a variety of other elements can be included within thecontrol system 200 to, e.g., further condition and process the signalsmeasured in the coil device 100. Just a few examples include additionalamplifying or filtering elements and means for subtracting out asubstantial DC or constant component (corresponding to the total volumeof the body inside the coils) in the signals so that only changes involume are detected. The volume signal can also be processed to detectrespiratory cycles, and determine the frequency of respiration, tidalvolume and a range of variables used in clinical spirometry. Inaddition, the rate of air flow in and out of the lungs can be calculatedby differentiating the volume signal as a function of time.

FIG. 12 is a flow diagram illustrating a method of measuring a volume ofa subject. For example, the method may be useful for measuring a volumeof a subject's abdomen and/or chest. In some cases the method includesproviding (170) a coil device according to an embodiment of theinvention, such as one of the coil devices 10, 100 described hereinhaving at least a first member and a first conductor. The first memberis then extended (172) around an outer surface of a first portion of thesubject's abdomen and/or chest. In so doing, the first member isconformed to the outer surface despite changes in a contour of the outersurface. The first conductor is preferably extended only once around thesubject's abdomen and/or chest.

Either before or after providing the coil device and extending it aroundthe subject, the method includes generating (174) with an electromagneta relatively homogeneous magnetic field throughout a predefined spatialvolume. For example, an alternating current may be fed to anelectromagnet to generate a time-varying, relatively homogeneousmagnetic field throughout the spatial volume. In some cases this meansthat the magnetic field has a coefficient of variation throughout thespatial volume of less than five percent variation. After generating thefield, the patient and coil device are positioned (176) within themagnetic field to induce a signal in the coil device. The induced signalis measured (178) by a connected control system, which can then estimate(180) a volume of the subject's abdomen and/or chest using the inducedand measured signal.

In some embodiments, a second member having a second conductor may alsobe extended around an outer surface of a second portion of the subject'sabdomen and/or chest. After positioning the second portion of thesubject's abdomen and/or chest within the spatial volume and magneticfield, a signal induced in the second conductor can be measured and usedto estimate a volume of the second portion. As indicated above, the coildevice may be used to measure the volume of a variety of areas of thesubject. In one case, the first portion is at least part of thesubject's abdomen and not part of the subject's chest. Corresponding tothis arrangement, the second portion may be at least part of thesubject's chest and not part of the subject's abdomen.

As previously discussed with reference to the figures, in some cases thesignal measured in the first and/or second conductors corresponds to anaverage cross-sectional area of the first and second portions of thesubject, respectively. In some embodiments, methods of the inventionfurther include estimating the volume of the first and/or secondportions by multiplying the average cross-sectional area (as representedby the measured signals) by a proportionality constant, such as thewidth of the first or second members, as explained with reference toFIG. 6.

In some embodiments of the invention, the authorization data stored inthe electronic memory 160 (see FIG. 10) can be used to secure the volumemeasuring process. For example, an operator may only be able to measurea volume of a subject if the authorization data indicates use of theparticular patient coil device is authorized. Referring now to FIG. 13,some embodiments of the invention further provide for reading (182) theauthorization data from the electronic memory and determining (184) fromthe authorization data whether use of the coil device is authorized. Ifuse of the coil device is authorized, the method can further includemeasuring (178) the signals induced in the coil device and estimating(180) the volumes associated with those signals.

Of course, a number of variations related to the authorization data arepossible. One or more steps in the process may be preconditioned uponauthorization of the coil device. As just one example, in some cases thesignal induced in the conductor(s) of the coil device may only bemeasured if use of the coil device is authorized.

In some embodiments, authorizing the coil device may include determiningwhether the coil device has exceeded a predetermined maximum number ofauthorized uses. For example, the authorization data may include amaximum count corresponding to the maximum number of authorized uses anda current count corresponding to an actual number of uses of the coildevice. The current count can be compared with the maximum count todetermine if the device is authorized for use. In further embodiments,the current count may be incremented after a use of the coil device bywriting to the electronic memory to change the current count. This canallow the coil device to track the number of times it has been used.

In additional embodiments, a stored identifier within the electronicmemory can associate a particular coil device with a particular subject.For example, a subject identifier can be assigned to the subject beingmonitored with the coil device and then stored in the electronic memoryto associate the subject with the coil device. Upon later using the coildevice, the device may first be authorized by comparing a subjectidentifier for the current subject with the stored identifier within theelectronic memory. Use of the coil device may only be authorized if thetwo identifiers match.

Thus, embodiments of the Coil System And Method For Obtaining VolumetricPhysiological Measurements are disclosed. Although the present inventionhas been described in considerable detail with reference to certaindisclosed embodiments, the disclosed embodiments are presented forpurposes of illustration and not limitation and other embodiments of theinvention are possible. One skilled in the art will appreciate thatvarious changes, adaptations, and modifications may be made withoutdeparting from the spirit of the invention and the scope of the appendedclaims.

1. A coil device for use in measuring a volume of a subject's abdomenand/or chest, the coil device comprising: a first member adapted toextend around an outer surface of a first portion of the subject'sabdomen and/or chest and conform to the outer surface despite changes ina contour of the outer surface, the first member comprising a firstconductor adapted to extend only once around the subject's abdomenand/or chest, the first conductor adapted to generate, in the presenceof a relatively homogeneous magnetic field produced by an energizedelectromagnet, a signal indicative of a volume of the first portion ofthe subject's abdomen and/or chest.
 2. The coil device of claim 1,wherein the first member comprises (i) first and second opposed edges,with the first edge being nearer the subject's head, and (ii) first andsecond opposed end sections adapted to be positioned proximate to oneanother and secured to conform the first member to the outer surface,and wherein the first conductor comprises a plurality of angled segmentsextending between the first and second opposed edges at multiple pointsbetween the first and second opposed end sections.
 3. The coil device ofclaim 2, wherein the plurality of angled segments form a zigzagconfiguration.
 4. The coil device of claim 2, wherein a cross-sectionalarea of the subject's abdomen and/or chest varies between the first andsecond opposed edges of the first member and the signal generated by thefirst conductor corresponds to an average cross-sectional area of thefirst portion of the subject's abdomen and/or chest.
 5. The coil deviceof claim 4, wherein the signal generated by the first conductor isgenerally proportional to the volume of the first portion of thesubject's abdomen and/or chest, with an approximate proportionalityconstant of a distance between the first and second opposed edges of thefirst member.
 6. The coil device of claim 1, further comprising a secondmember adapted to extend around an outer surface of a second portion ofthe subject's abdomen and/or chest and conform to the outer surface ofthe second portion despite changes in a contour of the outer surface ofthe second portion, the second member comprising a second conductoradapted to extend only once around the subject's abdomen and/or chest,the second conductor adapted to generate, in the presence of arelatively homogeneous magnetic field produced by an energizedelectromagnet, a signal indicative of a volume of the second portion ofthe subject's abdomen and/or chest.
 7. The coil device of claim 6,wherein the first portion is at least part of the subject's abdomen andnot part of the subject's chest, and wherein the second portion is atleast part of the subject's chest and not part of the subject's abdomen.8. The coil device of claim 1, further comprising an elastic substratecarrying the first member.
 9. The coil device of claim 8, furthercomprising a second member carried by the elastic substrate, the secondmember adapted to extend around an outer surface of a second portion ofthe subject's abdomen and/or chest and conform to the outer surface ofthe second portion despite changes in a contour of the outer surface ofthe second portion, the second member comprising a second conductoradapted to extend only once around the subject's abdomen and/or chest,the second conductor adapted to generate, in the presence of arelatively homogeneous magnetic field produced by an energizedelectromagnet, a signal indicative of a volume of the second portion ofthe subject's abdomen and/or chest.
 10. The coil device of claim 9,wherein the first portion is at least part of the subject's abdomen andnot part of the subject's chest, and wherein the second portion is atleast part of the subject's chest and not part of the subject's abdomen.11. The coil device of claim 9, wherein the elastic substrate comprises(i) first and second opposed edges, with the first edge being nearer thesubject's head, and (ii) first and second opposed end sections adaptedto be positioned proximate to one another and secured to conform theelastic substrate to the outer surface, wherein the first and secondconductors extend between the first and second end sections, and furthercomprising a common third conductor extending between the first andsecond end sections, wherein the first and second conductors areelectrically coupled to the third conductor proximate the second endsection of the elastic substrate.
 12. The coil device of claim 11,wherein the first, second, and third conductors exit the substrate at acommon area proximate the first end section of the substrate.
 13. Thecoil device of claim 11, wherein the third conductor is adapted toextend around an outer surface of a third portion of the subject, thethird portion having a relatively constant volume.
 14. The coil deviceof claim 13, wherein the third conductor is carried by the elasticsubstrate adjacent to the second edge of the elastic substrate.
 15. Thecoil device of claim 8, wherein the first conductor is plastic welded,glued, or stitched to the elastic substrate.
 16. The coil device ofclaim 8, wherein the elastic substrate comprises (i) first and secondopposed edges, with the first edge being nearer the subject's head, and(ii) first and second opposed end sections adapted to be positionedproximate to one another and secured to conform the elastic substrate tothe outer surface, wherein the first and second end sections are securedby a fastener selected from the group consisting of hook-and-loopfasteners, adhesive tape, buttons, staples, and zippers.
 17. The coildevice of claim 1, further comprising an elastic substrate carrying thefirst member, wherein the elastic substrate comprises a sleeve adaptedto fit around the first portion of the subject's abdomen and/or chest.18. The coil device of claim 1, further comprising an electronic memorystoring authorization data for determining whether use of the coildevice is authorized.
 19. A coil device for use in measuring a volume ofa subject's abdomen and/or chest, the coil device comprising: a firstmember adapted to extend around an outer surface of a first portion ofthe subject's abdomen and/or chest, the first member comprising (a)first conforming means for conforming the first member to the outersurface of the first portion despite changes in a contour of the outersurface of the first portion, and (b) first conducting means forgenerating, in the presence of a relatively homogeneous magnetic fieldproduced by an energized electromagnet, a signal indicative of a volumeof the first portion of the subject's abdomen and/or chest.
 20. The coildevice of claim 19, wherein the first conducting means comprises asingle conductor adapted to extend only once around the subject'sabdomen and/or chest.
 21. The coil device of claim 20, wherein the firstconforming means comprises an elastic substrate carrying the firstmember.
 22. The coil device of claim 19, further comprising: a secondmember adapted to extend around an outer surface of a second portion ofthe subject's abdomen and/or chest, the second member comprising (a)second conforming means for conforming the second member to the outersurface of the second portion despite changes in a contour of the outersurface of the second portion, and (b) second conducting means forgenerating, in the presence of a relatively homogeneous magnetic fieldproduced by an energized electromagnet, a signal indicative of a volumeof the second portion of the subject's abdomen and/or chest.
 23. Thecoil device of claim 22, wherein the first portion is at least part ofthe subject's abdomen and not part of the subject's chest, and whereinthe second portion is at least part of the subject's chest and not partof the subject's abdomen.
 24. The coil device of claim 22, furthercomprising an elastic substrate carrying the first and second members,wherein both the first and second conforming means comprise the elasticsubstrate.
 25. The coil device of claim 24, wherein the elasticsubstrate comprises (i) first and second opposed edges, with the firstedge being nearer the subject's head, and (ii) first and second opposedend sections adapted to be positioned proximate to one another andsecured to conform the elastic substrate to the outer surface, whereinthe first and second conducting means extend between the first andsecond end sections, and further comprising a common third conductingmeans extending between the first and second end sections, wherein thefirst and second conducting means are electrically coupled to the thirdconducting means proximate the second end section of the elasticsubstrate.
 26. The coil device of claim 25, further comprisingconnecting means, wherein the first, second, and third conducting meansare electrically coupled to the connecting means, and wherein the first,second, and third conducting means exit the substrate at a common areaproximate the first end section of the substrate.
 27. The coil device ofclaim 19, further comprising authorization means for determining whetheruse of the coil device is authorized.
 28. The coil device of claim 27,further comprising an electronic memory, wherein the authorization meanscomprises authorization data stored in the electronic memory.
 29. Amethod for measuring a volume of a subject's abdomen and/or chest,comprising: providing a coil device comprising a first member, the firstmember comprising a first conductor; extending the first member aroundan outer surface of a first portion of the subject's abdomen and/orchest, thereby conforming the first member to the outer surface despitechanges in a contour of the outer surface and extending the firstconductor only once around the subject's abdomen and/or chest;generating with an electromagnet a relatively homogeneous magnetic fieldthroughout a predefined spatial volume; positioning the first portion ofthe subject's abdomen and/or chest within the spatial volume; measuringa signal induced in the first conductor by the relatively homogeneousmagnetic field; and estimating a volume of the first portion of thesubject's abdomen and/or chest based on the signal measured in the firstconductor.
 30. The method of claim 29, wherein the coil device furthercomprises a second member comprising a second conductor, and furthercomprising: extending the second member around an outer surface of asecond portion of the subject's abdomen and/or chest, thereby conformingthe second member to the outer surface of the second portion despitechanges in a contour of the outer surface of the second portion andextending the second conductor only once around the subject's abdomenand/or chest; positioning the second portion of the subject's abdomenand/or chest within the spatial volume; measuring a signal induced inthe second conductor by the relatively homogeneous magnetic field; andestimating a volume of the second portion of the subject's abdomenand/or chest based on the signal measured in the second conductor. 31.The method of claim 30, wherein the first portion is at least part ofthe subject's abdomen and not part of the subject's chest, and whereinthe second portion is at least part of the subject's chest and not partof the subject's abdomen.
 32. The method of claim 29, wherein the signalmeasured in the first conductor corresponds to an averagecross-sectional area of the first portion of the subject's abdomenand/or chest, wherein the first member has first and second opposededges, with the first edge being nearer the subject's head, and furtherwherein estimating the volume of the first portion comprises multiplyingthe average cross-sectional area by a distance between the first andsecond opposed edges of the first member.
 33. The method of claim 29,further comprising enabling use of the coil device only if use of thecoil device is authorized.
 34. A method for measuring a volume of asubject's abdomen and/or chest, comprising: providing a coil devicecomprising an electronic memory storing authorization data; positioningthe coil device around an outer surface of a first portion of thesubject's abdomen and/or chest; reading the authorization data from theelectronic memory; determining from the authorization data whether useof the coil device is authorized; generating with an electromagnet arelatively homogeneous magnetic field throughout a predefined spatialvolume; positioning the first portion of the subject's abdomen and/orchest within the spatial volume; and if use of the coil device isauthorized, estimating a volume of the first portion of the subject'sabdomen and/or chest, based on a signal induced in the first conductorby the relatively homogeneous magnetic field.
 35. The method of claim34, further comprising measuring the signal induced in the firstconductor only if use of the coil device is authorized.
 36. The methodof claim 34, wherein the coil device further comprises a first membercomprising a first conductor, and wherein positioning the coil devicecomprises extending the first member around the outer surface of thefirst portion of the subject's abdomen and/or chest, thereby conformingthe first member to the outer surface despite changes in a contour ofthe outer surface and extending the first conductor only once around thesubject's abdomen and/or chest.
 37. The method of claim 34, whereindetermining whether use of the coil device is authorized comprisesdetermining whether the coil device has exceeded a maximum number ofauthorized uses.
 38. The method of claim 37, wherein the authorizationdata comprises a maximum count corresponding to the maximum number ofauthorized uses and a current count corresponding to an actual number ofuses of the coil device, and wherein determining whether use of the coildevice is authorized comprises comparing the current count with themaximum count.
 39. The method of claim 38, further comprisingincrementing the current count after a use of the coil device.
 40. Themethod of claim 34, further comprising assigning a subject identifier tothe subject and storing the subject identifier in the electronic memoryas a stored identifier, and wherein determining from the authorizationdata whether use of the coil device is authorized comprises comparingthe subject identifier with the stored identifier.
 41. The method ofclaim 34, wherein the electronic memory further comprises aproportionality constant corresponding to the coil device, and furthercomprising estimating the volume of the first portion of the subject'sabdomen and/or chest based on the induced signal and the proportionalityconstant.
 42. A system for measuring a volume of a subject's abdomenand/or chest, comprising: an electromagnet adapted to generate arelatively homogeneous magnetic field within a predefined spatialvolume; a coil device comprising an electronic memory storingauthorization data, the coil device adapted to conform to an outersurface of a first portion of the subject's abdomen and/or chest andgenerate, in the presence of the relatively homogeneous magnetic fieldproduced by the electromagnet, a signal indicative of a volume of thefirst portion of the subject's abdomen and/or chest; and a controlsystem electrically coupled to the coil device, the control systemadapted to read the authorization data from the electronic memory,determine from the authorization data whether use of the coil device isauthorized, measure the signal generated by the first conductor, and ifuse of the coil device is authorized, estimate the volume of the firstportion of the subject based on the signal received from the firstconductor.
 43. The system of claim 42, wherein the coil device furthercomprises a first member adapted to extend around the outer surface andconform to the outer surface despite changes in a contour of the outersurface, the first member comprising a first conductor adapted to extendonly once around the subject's abdomen and/or chest.
 44. The system ofclaim 42, wherein the control system measures the signal generated bythe coil device only if use of the coil device is authorized.
 45. Thesystem of claim 42, wherein the authorization data comprises a maximumcount corresponding to a maximum number of authorized uses of the coildevice and a current count corresponding to an actual number of uses ofthe coil device, and wherein control system is adapted to compare thecurrent count with the maximum count.
 46. The system of claim 45,wherein the control system is adapted to increment the current countafter a use of the coil device.
 47. The system of claim 42, wherein theauthorization data comprises a stored identifier and the control systemis adapted to compare the stored identifier with a subject identifierassigned to the subject.
 48. The system of claim 42, wherein theelectronic memory further comprises a proportionality constantcorresponding to the coil device, and wherein the control system isadapted to estimate the volume of the first portion of the subjectadditionally based on the proportionality constant.